Preparation of pigmentary form isoindoline

ABSTRACT

A process for converting finely particled agglomerated crude isoindoline pigments of the formula ##STR1## where A is ##STR2## and B is the radical of an unsubstituted or substituted barbituric acid, or A and B are both such a barbituric acid radical, into tinctorially valuable pigmentary forms, wherein the crude pigment, which consists of primary particles having a mean size of ≦0.1 μm, is subjected to shearing forces in water, and thereafter the aqueous suspension is heated at from 90° to 160° C. in the presence or absence of a surfactant and the pigment is isolated. Easily dispersible, low-hiding to extremely high-hiding pigments are obtained, which give brilliant colorations of improved lightfastness and fastness to weathering.

This is a continuation of application Ser. No. 1272, filed Jan. 5, 1979,now U.S. Pat. No. 4,271,301.

The present invention relates to a process for converting an isoindolinepigment into an easily dispersible, brilliant, low-hiding to extremelyhigh-hiding and weathering-fast pigmentary form.

Isoindoline pigments of the formula ##STR3## where A is ##STR4## or isthe radical of a barbituric acid and B is the radical of a barbituricacid (for example the compound described in British Pat. No. 1,187,667.

Example 76, and especially those in which both A and B are a barbituricacid radical, for example the compounds described in German Laid-OpenApplication DOS 2,041,999 are distinguished by good fastnesscharacteristics. It is true that the pigments obtained by the methods ofpreparation described in the above publications are obtained in a finelyparticled form, but the pigments are agglomerated and harsh in textureso that the colorations obtained in surface coatings and plastics arespecked, pale and dull and have low hiding power.

Using the customary methods of preparation of high-hiding organicpigments, such as heating the crude pigment in an organic solvent in thepresence or absence of water (German Laid-Open Applications DOS2,521,249, 2,302,508, 2,302,517, 2,302,482 and 2,521,249) or milling thepigment and then recrystallizing it from an organic solvent as describedin German Laid-Open Application DOS 2,357,077, does not succeed, in thecase of the above isoindoline compounds, in producing the desiredpigmentary form.

It will be appreciated from the Examples which follow that the presentinvention provides a process in which the above isoindoline compoundscan be converted into brilliant, easily dispersible and high-hidingpigmentary forms whilst retaining or improving the fastnesscharacteristics.

According to the invention, there is provided a process for thepreparation of a pigmentary form of an isoindoline pigment of thegeneral formula: ##STR5## wherein A is ##STR6## or is the radical of abarbituric acid and B is the radical of a barbituric acid, wherein theagglomerated crude pigment, in which the primary particles have a meanparticle size of ≦0.1 μm, is subjected to shearing forces in an aqueousmedium, thereafter the resulting aqueous suspension is heated at from90° to 160° C. in the presence or absence of a surfactant, and thepigment is isolated.

The barbituric acid radicals may, for example, be the radicals ofN-methylbarbituric acid, N-phenylbarbituric acid, 2-thiobarbituric acid,2-iminobarbituric acid, 2-N-cyanoiminobarbituric acid or unsubstitutedbarbituric acid. Of course, when two radicals of a barbituric acid arepresent they may be identical or different and naturally the startingpigment may comprise two isoindolines differing with respect to theidentity of barbituric acid radicals in their molecules. The radical ofunsubstituted barbituric acid is preferred.

Using the process of the invention, it is possible, simply and withoutemploying an organic solvent (and thus avoiding the economic andecological problems associated with the use of organic solvents), toobtain brilliant, easily dispersible and low-hiding to extremelyhigh-hiding pigments having improved lightfastness and fastness toweathering.

The process according to the invention is in general carried out bysubjecting the crude isoindoline pigment (which may, for example, havebeen prepared in accordance with German Laid-Open Application DOS2,041,999 or British Pat. No. 1,187,667) to shearing forces in thepresence of water at from 20° C. to 100° C.

In the methods of isoindoline preparation described in the citedliterature, the crude pigments are obtained in a very finely particledform and can normally be subjected, as obtained, to the processaccording to the invention. However, where crude pigments with a meanprimary particle size >0.1 μm are concerned, comminution to a meanprimary particle size of ≦0.1 μm, preferably having a very narrowparticle size distribution, is necessary.

Particularly valuable products are obtained if, before carrying out theprocess according to the invention, the crude pigments are comminuted inthe conventional manner by milling to a mean primary particle size of≦0.02 μm coupled with a very narrow particle size distribution.

The shearing forces in the aqueous suspension are generated, forexample, in comminuting equipment employing an agitated grinding mediumsuch as glass, metal, ceramic or plastics balls, or sand. Examples ofsuch comminuting equipment are a sand mill, a bead mill, and a stirredball mill. The required shearing forces may also be applied using akneader.

The amount of the grinding medium when used is in general from 10 to 40times the amount by weight of the pigment.

As mentioned earlier, the shear is normally carried out at from 20° C.to 100° C., but preferably it is effected at from 40° to 80° C.

The aqueous pigment suspension produced by the shearing is heated (inthe presence of the grinding medium or after removal thereof) eitherdirectly or after addition of a surfactant, at from 90° C. to 160° C.,and can then be worked up in a conventional manner.

The amount of surfactant when used is not critical and can be variedwithin wide limits. Thus, even less than 1%, based on pigment, sufficesto ensure good wetting of the pigment whilst it is being heated.Usually, however, when used the surfactant will be used in an amount offrom 1% to 100%, based on pigment.

The surfactant may, for example, be a nonionic, anionic or cationiccompound conventionally used as a dispersant, wetting agent and/orprotective colloid. Examples of anionic surfactants are alkali metalsalts or alkaline earth metal salts or ammonium salts of C₄ -C₂₀-alkylbenzenesulfonic acids, C₄ -C₂₀ -alkylphenolsulfonic acids, mono-and bis-C₁ -C₁₀ -alkylnaphthalenesulfonic acids, partially sulfonatedpolystyrene, water-soluble condensation products ofβ-naphthalenesulfonic acid and/or C₁ -C₁₀ -alkylnaphthalene-β-sulfonicacids with formaldehyde, condensation products of phenolsulfonic acids,formaldehyde and urea, condensation products of phenol, urea and sodiumsulfite, phenol-formaldehyde condensation products which have beenpost-condensed with phenolsulfonic acid, urea and formaldehyde,ligninsulfonic acids, long-chain C₁ -C₂₀ -fatty acids and rosin acids.

Examples of nonionic surfactants are adducts of ethylene oxide,propylene oxide or ethylene oxide and propylene oxide with C₈ -C₂₀-alkanols, C₂ -C₁₀ -alkanediols, C₃ -C₁₀ -alkanepolyols, phenols, C₆-C₁₈ -alkylphenols, C₈ -C₂₀ -carboxylic acids, C₈ -C₂₀ -carboxylic acidamides and aliphatic, cycloaliphatic or benzene-aromatic monoamines,diamines and polyamines.

Further examples of the surfactants are water-swellable andwater-soluble polymers, for example copolymers of vinylpyridine,N-vinylpyrrolidine, acrylamide and/or acrylic acid with one or morewater-insoluble monomers, eg. acrylonitrile, methacrylic acid esters,acrylic acid esters, vinyl acetate, vinyl chloride and/or styrene, aswell as polyvinyl alcohol, and C₁₀ -C₂₀ -fatty alcohols.

The surfactant can, of course, be used in the form of a mixture.

Preferred surfactants are alkali metal or ammonium salts of C₁ -C₅-alkylnaphthalenesulfonic acids, condensation products of phenol, ureaand formaldehyde, adducts of ethylene oxide, propylene oxide and/orethylene oxide and propylene oxide with C₂ -C₂₀ -alkanols, C₂ -C₁₀-alkanediols, C₃ -C₁₀ -alkanetriols, aliphatic C₁₀ -C₂₀ -carboxylicacids and their amides and C₁₀ -C₂₀ -fatty alcohols, and mixtures ofthese.

By appropriate selection of the conditions for heating the aqueoussuspension, after it has been subjected to shearing forces, it ispossible to produce, in a controlled manner, high-hiding and veryhigh-hiding pigments having very good tinctorial and technologicalproperties.

If, after milling, the suspension is boiled for from one to ten hours,brilliant, deep and low-hiding pigments are obtained.

If the same suspension is refluxed for from 10 to 30 hours, especiallyfrom 15 to 30 hours, brilliant more highly hiding pigments havingimproved lightfastness and fastness to weathering are obtained.

If, after milling, the suspension is heated for from 3 to 20 hours atfrom 110° to 140° C. under pressure, the pigments obtained are extremelyhigh-hiding compared to conventional organic yellow pigments and haveexcellent lightfastness and fastness to weathering.

The Examples which follow illustrate the process according to theinvention. Parts and percentages in the Examples are by weight.

EXAMPLE 1

30 parts of the colorant described in Example 1 of German Laid-OpenApplication DOS 2,041,999 are milled for 8 hours in a planetary ballmill (filled with 150 parts of agate balls of diameter from 0.5 to 1.5cm), the resulting primary particle size being ≦0.05 μm. The greatlydensified, brownish yellow powder is stirred with 180 parts of plasticbeads of diameter from 0.5 to 1 mm and 240 parts of water for 5 hours atfrom 60° to 70° C., using a high-speed stirrer. The beads are thensieved off and washed with a further 200 parts of water to removeadhering colorant.

0.5 part of the sodium salt of a C₁ -C₅ -alkylnaphthalenesulfonic acidis added to the resulting suspension, which is then heated for 7 hoursat 130° C. After filtration and drying, 25 parts of a brilliant, easilydispersible and high-hiding very reddish yellow pigment having excellentlightfastness and fastness to weathering are obtained.

EXAMPLE 2

The procedure described in Example 1 is followed, except that thepigment suspension is heated for 14 hours at 100° C. 26 parts of areddish, deep and easily dispersible yellow pigment of medium hidingpower, significantly improved fastness to weathering and greatbrilliance in pure shades are obtained.

EXAMPLE 3

The procedure described in Example 1 is followed, except that thepigment suspension is heated for 6 hours at 100° C. 27 parts of a verydeep, brilliant pigment are obtained; this product is significantlysuperior, in hiding power and dispersibility, to the pigment obtainableaccording to Example 1 of German Laid-Open Application DOS 2,041,999.

EXAMPLE 4

The procedure described in Example 1 is followed, but a crude pigmentprepared as described in Example 1 of German Laid-Open Application DOS2,041,999 is used for milling in water. 24 parts of a brilliant, easilydispersible and high-hiding very reddish yellow pigment having excellentlightfastness and fastness to weathering are obtained.

A yellow pigment with the same properties is obtained if the crudepigment used is that obtained according to Example 2 or Example 3 ofGerman Laid-Open Application DOS 2,041,999.

EXAMPLE 5

The procedure described in Example 1 is followed, except that 30 partsof the pigment prepared as described in Example 76 of British Pat. No.1,187,667 are used. 24 parts of a brilliant, high-hiding and easilydispersible greenish pigment are obtained, the pigment being fast toweathering in colorations near the pure shade.

We claim:
 1. A process for the preparation of a brilliant, easilydispersible and low-hiding to extremely high-hiding pigmentary form ofan isoindoline pigment of the formula ##STR7## wherein A is ##STR8## oris a substituted or unsubstituted barbituric acid radical, and B is asubstituted or unsubstituted barbituric acid radical, whichcomprisessubjecting a suspension which consist essentially of theagglomerated crude pigment, in which the primary particles have a meanparticle size of ≦0.1 μm to shearing forces in water in the presence ofgrinding media or in a kneader, thereafter heating the resulting aqueoussuspension at from 90 to 160 C in the presence or absence of asurfactant, for 1-30 hours and isolating the resulting pigment.
 2. Aprocess as claimed in claim 1, wherein an agglomerated crude pigment inwhich the primary particles have a mean particle size of ≦0.02 μm, isemployed.
 3. A process as claimed in claim 1 or 2, wherein the shearingforces are generated in the aqueous suspension of the fine-particledagglomerated crude pigment by means of agitated milling bodies.
 4. Aprocess as claimed in claim 1 or 2, wherein a crude pigment is used inwhich A is ##STR9## and B is a radical of unsubstituted barbituric acid,of N-phenylbarbituric acid, of 2-thiobarbituric acid, of2-iminobarbituric acid or of 2-N-cyanoiminobarbituric acid, or A and Bare each one of the radicals mentioned in the definition of B.
 5. Aprocess as claimed in claim 1 or 2, wherein A and B are each a radicalof unsubstituted barbituric acid or A is ##STR10## and B is the radicalof unsubstituted barbituric acid.
 6. A process as claimed in claim 1 or2, wherein the aqueous suspension is heated in the presence of an adductof ethylene oxide, propylene oxide or propylene oxide and ethylene oxidewith a C₈ -C₂₀ -alkanol, C₂ -C₁₀ -alkanediol, C₃ -C₁₀ -alkanepolyol,phenol, C₆ -C₁₈ -alkylphenol, C₈ -C₂₀ -carboxylic acid, C₈ -C₂₀-carboxylic acid amide or aliphatic, cycloaliphatic or benzene-aromaticmonoamine, diamine or polyamine.
 7. A process as claimed in claim 1 or2, wherein the aqueous suspension is heated in the presence of an alkalimetal salt or ammonium salt of a C₄ -C₂₀ -alkylbenzenesulfonic acid, C₄-C₂₀ -alkylphenolsulfonic acid, mono- or bis-C₁ -C₁₀-alkylnaphthalenesulfonic acid, partially sulfonated polystyrene,water-soluble condensation product of β-naphthalenesulfonic acid or of aC₁ -C₁₀ -alkylnaphthalene-β-sulfonic acid, or of a mixture of these,with formaldehyde, condensation product of a phenolsulfonic acid,formaldehyde and urea, ligninsulfonic acid or C₇ -C₂₀ -rosin acid.
 8. Aprocess as claimed in claim 4, wherein the aqueous suspension is heatedin the presence of an alkali metal or ammonium salt of a C₁ -C₅-alkylnaphthalenesulfonic acid, a condensation product of phenol, ureaand formaldehyde, an adduct of ethylene oxide, propylene oxide orpropylene oxide and ethylene oxide with a C₂ -C₂₀ -alkanol, C₃ -C₁₀-alkanediol, aliphatic C₁ -C₂₀ -carboxylic acid or aliphatic C₁ -C₂₀-carboxylic acid amide, C₁₀ -C₂₀ -fatty alcohol or a mixture of the saidagents as the surfactant.
 9. A process as claimed in claim 8, whereinthe amount of surfactant, based on crude pigment, is from 1 to 100% byweight.
 10. The process of claim 1, wherein said heating is carried outfor 1-10 hours.